All hydraulic cutter with spring knife return



Nov. 12, 1968 C. THUMIM 4 Sheets-Sheet ALL HYDRAULIC CUTTER WITH SPRINGKNIFE RETURN Filed March l0, 1966 Nov. 12, 1968 c. THUMIM 3,410,155

ALL HYDRAULIC CUTTER WITH SPRING KNIFE RETURN Filed March lO, 1966 4Sheets-Sheet 2 Nov. 12, 1968 C. THUMIM 3,410,166

ALL HYDRAULIC CUTTER WITH SPRING KNIFE RETURN Filed March l0, 1966 4Sheets-Sheet 3 1N VEN TOR V7/FL THUM/M NOV. 12, THUMIM ALL HYDRAULICCUTTER WITH SPRING KNIFE RETURN Filed March lO, 1966 4 Sheets-Sheet 4United States Patent O 3,410,166 ALL HYDRAULIC CUTTER WITH SPRING KNIFERETURN Carl Thumim, Chicago, Ill., assignor to Miehle-Goss- Dexter,Incorporated, Chicago, Ill., a corporation f Delaware Filed Mar. 10,1966, Ser. No. 533,178 13 Claims. (Cl. 83-380) ABSTRACT 0F THEDISCLOSURE A cutting machine of the guillotine type which includes aclamp operated entirely by a hydraulic system, and a knife operative inits cutting stroke by hydraulic means but returned to its rest positionby spring biasing means. The hydraulic system includes a large capacityand a small capacity pump which are cumulative in effect when the knifeand clamp are being operated but requires only the small capacity pumpto retain the clamp in its upward or rest position between cuttingcycles.

This invention relates to guillotine-type paper cutters, and moreparticularly to a cutter in which knife return iS effected by a spring.

Among the objects of the invention are to provide a simplified hydraulicsystem and electric control circuitry for a hydraulic paper cutter; toprovide for economy of operation by reducing the oil pressure and thequantity of oil circulating under pressure in the hydraulic systembetween cutting operations; to provide for operator safety in that twohands are required to effect actuation ofthe clamp and knife; to provideoptionally for convenient operation in that once the knife has startedmoving the operator may free one hand; to provide an arrangement using ahigh capacity pump and low capacity pump in which both pumps providepressure for actuating the clamp and the knife, thereby effecting apower saving and a simplicity of construction, but wherein only the lowcapacity pump is required to maintain the clamp in raised position.

Other objects and features of the invention will be apparent from thedescription that follows, a particular object being to provide a simplemechanism wherein a spring effects a return movement of the knife.

Referring to the drawings;

FIGURE 1 is a diagrammatic illustration of the mechanical arrangementutilizing hydraulic cylinders for operating the clamp and knife andshowing the use of a spring for effecting knife return;

FIGURE 2 is a fragmentary illustration in elevation partially in sectionshowing certain components of the knife actuating mechanism;

FIGURE 3 is an end view partially in section showing certain componentsillustrated in FIGURE 2;

FIGURE 4 is a plan view illustrating, partially in section, certaincomponents shown in FIGURE 2;

FIGURE 5 is an electrical diagram showing circuitry control for thenovel aspects of the invention; and

FIGURE 6 is a hydraulic circuit diagram illustrating the pump and valvearrangement to effect actuation of the knife and clamp.

Referring to FIGURE 1, a knife bar 10 is illustrated which will beunderstood to be reciprocal in a vertical plane being guide by fixedpins 12 acting in slots 15 of the knife bar in a conventional manner.The knife bar carries a knife 18 secured thereto and is actuated by apull bar 22, all in a conventional manner.

A clamp 25 is illustrated which will be understood to be conventionallyoperated as by pull bars 28 acting through a link 32 and bellcranks 35and 38 powered by a Patented Nov. 12, 1968 double ended hydrauliccylinder 40 connected to bellcrank 35 and having pressure chambers 43and 46.

The arrangement for effecting actuation of the knife pull bar 22 isbelieved to be unique and comprises a single ended hydraulic cylinder50, having a pressure chamber 53 and a piston rod connected to abellcrank lever 56 which is provided with three arms. Thus the arm 56Ais connected to the piston rod while the arm 56B is connected to a rod60 concentric within a compression spring 63 and arranged so thatmovement of the rod toward the right will compress the spring. The thirdarm 56C is connected to operate the knife bar linkage in a conventionalmanner but is disposed so that upon swinging counterclockwise when thecylinder 50 is put under pressure the end of the arm 56C will abut adash pot 67 which serves as a cushion and motion limit stop at the endof the knife stroke, as indicated by the phantom lines illustrating thelimit of downward movement of arm 56C. The rod 60 will be understood tobe slidably supported in a fixed wall 70 which is part of the machineframe F indicated by the phantom line.

The outer end of rod 60 is disposed to abut a fixed rubber bumper pad 73when the spring 63 is fully extended to serve as a cushion for limitingmovement of the knife at top position.

In operation, the chamber 43 is filled with oil under pressure to causethe clamp to come down against a paper pile resting on a table 78, allin the usual manner. The nvention contemplates knife actuation onlyafter a predetermined degree of pressure is brought to bear by the clampon the paper pile, and this feature will be subsequently explained inconnection with the hydraulic circuit. Upon predetermined pressure beingapplied by the clamp, the knife is actuated by pressure conducted tocylinder chamber 53 which rocks the bellcrank 56 counter-clockwiseoperating the knife bar linkage and at the same time compressing thespring 63 via arm 56B until the downward movement of the knife isstopped by arm 56C abutting dash pot 67. On the return stroke of theknife, pressure being exhausted from chamber 53, the spring 63 expandsto rock the bellcrank lever 56 clockwise, moving the knife upwardlyuntil the end of rod 60 abuts rubber bumper 73.

FIGURES 3, 4 and 5 show details of component construction and theirrelationship to each other insofar as essential elements are concerned.For example, in FIG- URE 2 the three-arm bellcrank 56 is illustrated aspivotal on a pin 82 which is carried at one end in a plate 85 (FIGURE 4)fastened to the machine frame F and has bearing in a journal 88 machinedinto a wall 90 of the frame, as seen in FIGURE 3. The spring 63 has itsouter end abutting in a cup 92 suitably pinned by means of pins to themachine frame as generally illustrated in FIGURE 4. The rod 60 has athreaded end and bolt 98 thereon which abuts on the opposite side of cup92 to limit spring expansion, it being understood that the rod isslidable in a bore through cup 92, which cup has ears 102 (FIGURE 3)through each of which passes the pins 10S to provide a pivotal mount forthe spring between the walls 90 and 108 of the machine frame.

The bellcrank lever S6 will be understood to be partially bifurca-ted sothat the arm 56C is in actuality a pair of parallel arms between whichthe pull bar 22 is pivotally fastened as by pin 112 (FIGURE 3). The arm56B is secured by pin 113 to a cap 116 to which the rod 60 is fastened,the cap having bifurcated walls 120 between which the lower end of thearm is disposed. The outer edges of walls about the rubber block 73which has a metal facing 122 vulcanized to the rubber block in turnvulcanized to a metal block 125 carried in a bracket 128. Bracket 128 ispart of the machine frame and metal block 125 may be adjusted axiallyrelative to 3 rod 60 by means of a screw 132 carried inthe block andabutable with bracket 128 (FIGURE 4). A` positive stop adjustable screw135 is carried in block 125 the end of which may be abutted by the lowerend of arm 56B to effect a positive top position for the knife bar afterthe cushioning effect of rubber block 73.

The piston rod for cylinder 50 (FGURES 2 and 3) is pivotally securedbetween bifurcations of arms 56A as by a pin 140 with the outer end ofthe cylinder being pivoted between ears, such as 143, of the machineframe by means of a pin 146 having bearing support in collars 149 and152.

Referring to FIGURE 5, the electrical control circuitry is disclosedshowing the main motor M to be controlled by the star-ting switch SW1 ina conventional manner, the power lines L1 and L2 being provided foractuation of the control circuitry for the motor and also foi solenoidvalves which control the oil pressure cylinders. The control circuitryhas left-hand and right-hand buttons, designated as LH and RH, whereinthe buttons must be pressed by the operators two hands in order toactuate the clamp and knife. Solenoid SOL-1 controls a fourway valve forthe clamp cylinder. Solenoid SOL-2 controls a valve for the knifecylinder and solenoid SOL-3 controls a two-way valve which provides formost of the oil being circulated in the hydraulic system under lowpressure when not actuating the power cylinders, thereby effecting apower saving and reducing the heating effect of the circulating oil.

Various microswitches are disposed to be actuated by the knife andclamp, For example, MS-l is a normally open switch which is closed bythe clamp when the clamp is in an upper position; MS-2 is a normallyclosed switch which is opened by the knife when the knife reaches itsbottom position', MS-3 is a normally closed switch which is opened bythe clamp in upper position and closes when the clamp starts to move.MS-4 is a normally closed switch opened by the knife at upper positionwhich closes once the knife has started to move. MS-S is a normallyclosed switch opened by the knife when the knife reaches its bottomposition. MS-6 is a normally closed switch opened when the knife startsits downward movement. MS-7 is a normally closed switch which is openedwhen the clamp reaches top position.

The securing of the several knife and clamp operated switches so as tobe knife or clamp operated is well known as are switch `constructionsand no mechanical d"- tails are necessary herein.

All switches are shown for the condition in which knife and clamp are atrest at stroke top.

The relay coil CR is normally energized via contacts of normallyreleased button switches LH and RH when the clamp and knife are inraised position in order to condition SOL-1 and SOL-2 for energizationvia relay CR contacts. Relay CR is deenergized when the knife completesits cutting stroke due to opening of MS-2 and MS-S. Thus, the solenoidscannot operate again until the relay is reset by releasing buttonswitches; LH and RH, and knife and clamp are in up positions, closingMS-2 and MS-l, respectively.

The main motor switch and starter system are shown at the top of FIGURE5, being conventional in nature and having a contact R-l which connectsthe control circuitry to power when the main motor is started, aseffected by relay R.

Assuming the main motor is running, the manually operable LH and RHbuttons released being spring biased to the position shown and relay CRis normally energized through switches MS-l and MS-2 and contacts A.This closes all CR contacts CRI, CRS and CRi. Switches MS-l, MS-2 andMS-S are closed at this time since the clamp is in upper position as isthe knife.

For operation, manual buttons LH and RH are pressed to complete acircuit through MS-Z, contacts Bfcontacts CRS and 4 and MS-S to energizethe clamp control valve solenoid SOL-1. This opens a four-way valve 215(FlGURE 6) to direct oil pressure to the chamber 43 of clamp cylinder 40(FIGURES l and 6). After the clamp starts to move it releases switchMS-l which will not close again until the clamp returns to its top restposition. The A contacts of the pushbuttons LH and RH open to break thecircuit to relay CR which, however, remains energized through MS2 andCRS. The clamp also releases MS-3 which then closes energizing controlvalve solenoid SOL-2 through MS-Z, contacts C, CR1, CR3 and MS-S.

Although the clamp is moving, the knife cannot move until the clamppressure on the paper pile has reached a predetermined value, thusproviding an interlock to prevent the knife from starting its motionbefore the paper pile is fully clamped. This is under non-electrichydraulic control as will be later described. Assuming the predeterminedpressure has been built up by the clamp on the paper pile, and sinceSOL-2 is energized, it opens a four-way valve 22! (FGURE 6) topressurize chamber 53 of knife cylinder 50. The knife commences movingdownwardly thereby permitting closure of switch MS-4 which locks clampsolenoid SOL-1 in energized condition independently of relay CR ContactCR4, although the relay remains energized. Continued movement of theknife to bottom position opens switches MS-2 and MS-S to deenergize therelay CR and SOL-2. Accordingly, all CR contacts open, SOL-2 isdeenergized and oil pressure ceases to chamber 53 of knife cylinder 50,but MS-4 remains closed, SOL-1 remains energized, the clamp maintainspressure.

The valves 215 and 220 are of a commercial type which are moved in onedirection by their solenoids but have internal springs (not shown) whichmove them in the opposite direction when their solenoids aredeenergized.

Oil pressures ceasing to flow to cylinder 50 and it being understoodthat the valve 22) is then actuated to its alternate position byinternal spring bias, exhaust of cylinder 5t) occurs through valves 275and 220 upon such deenergization of SOL-2. Spring 6) (FIGURE 1) whichwas compressed as the knife carne down, by virtue of the rocking ofbellcrank 56, expands to move the knife to top position. At top positionthe knife opens switch MS-4 to deenergize clamp Valve solenoid SOL-1thereby permitting reversal (due to its internal spring) of the four-wayvalve 215 which controls clamp movement. Such reversal effects movementof the valve to conduct oil under pressure to chamber 46 (FGURE 1) ofcylinder 40 effecting raising of the clamp, chamber 43 exhausting. Whenthe clamp reaches top position, relay CR could reset due to closing ofIMS-1, but the knife cannot recycle since buttons LH and RH are beingheld depressed which there-by prevents energization of relay CR due tothe open contacts A. Both hands must be removed from buttons LR and RHin order to reset the relay in energized condition. Thereafter, themachine can be recycled by pressing both buttons again.

The circuitry provides for a necessity that both hands of an operatorstart the cyciing of the machine but after being started one hand canmaintain the cycling if so desired. In order to accomplish this thenormally closed switch MS-6 may be disposed to be closed when the knifestarts its ldownward movement and the switch shunts the Contact C of theLH button. The clamp solenoid SOL-1 remains energized through MS-4 afterthe knife starts down. The LH button may then be released. Bymaintaining the RH button depressed SOL-2 will remain energized tocomplete the knife cycling. Switch MS- is, of course, maintained open bythe knife at top position so that two hands are required to start thecycle. If .MS-6 is not supplied, both hands must lbe kept on the buttonsfor full cuttings strokes.

The function of MSJ and SOL-3 is explained below in detail.

Referring to the hydraulic diagram of FIGURE 6, the system comprises atwin pump having a high capacity section P1 and low capacity section P2wherein the high capacity section has a -discharge volume ofapproximately ten times that of the low capacity section. Flow from bothsections are used in parallel Via outlet tube 221 for obtaining rapidaction during machine cycling. However, P1 has its output shuntedthrough a valve 222 to the tank, the valve 222 being normally openbetween cycling operations. At that time P2 maintains the clamp in topposition through line 225, reducing valve 22d, check valve 232, four-wayvalve 215, line 236, and check valve 140. Two-way valve 222 is biasedinternally to open when SAL-3 (FIGURE 5) is deenergized upon opening ofMS-7 when the clamp reaches top position. As the clamp starts down MS-'7closes to close valve 222 via SOL-3 so that full pumping capacity of P1and P2 is used in clamping and cutting.

The valve 228 is a pressure reducing valve which places a maximum limiton the outlet pressure of pumps P1 and P2 regardless of inlet pressure.In commercial practice such maximum pressure would be about 1200 poundsat the outlet even though pump pressure may rise to about 1500 pounds.Valve 228 can be adjusted for variable outlet pressures.

An auxiliary relief valve 243 is connected so as to control clamppressure when the clamp is moving down but has no affect when the clampis in top position.

When valve 215 is shifted by its internal spring (SOL-1 deenergized)pressure from pump P2 is maintained in chamber 46 of cylinder 40 to holdthe clamp in its upper position and pump P1 is shunted to the tank aspreviously mentioned. Sufficient clamp holding pressure is provided byadjustment of a relief Valve 252 so that there is enough force exerted-by cylinder 40 to just maintain and balance the clamp weight at the topof its stroke. This has the affect of maintaining pump section P1 at alow pressure which effects a saving of power and minimum of temperaturerise in the circulating oil.

Upon `energization of SOL-1, oil under pressure from valve 220 isconducted to chamber 43 to move the clamp down. The clamp dropsinitially of its own weight, oil being sucked into chamber 43 via theusual prefill valve 244. Speed of clamp drop can be regulated by the110W control valve 248 which has a needle valve for adjustment, Thecheck valve 232 prevents bounce of the clamp at each end of its stroke.The ow shunt to tank through valve 222 for pump 'P1 is closed by closingof MS-7 and energization of SOL-3.

Thus, when the clamp starts to move down, the combined capacity of thepumps sends a large flow of oil to the system. Oil from pump P1 goesthrough check valve 256 which otherwise prevents oil from pump P2 fromshunting through valve 222 when the clamp is held in raised position.

A relief valve 260 insures the system against excessive pressure.

As previously mentioned, the valve 228 maintains a pressure to clampcontrol valve 215 within certain limits for operation of the clamp and as-imilar valve 264 performs the same function for knife power. However,valve 264 is a so-called sequence valve which requires a predeterminedpressure to be exerted on it before passing the oil through to the knifecontrol valve 220. In commercial operation such pressure may be pre-setat about 1350 pounds. As was previously mentioned in connection withdescription of FIGURE 5, the energization of solenoid SOL-2 is withoutaffect on control of valve 220 prior to a predetermined clamp pressurebeing brought to bear on the paper pile. The pipe connection 270 in FIG-URE 6 from pressure chamber 43 to a pilot piston with which valve 220 isconventionally provided effects the desired function. Thus, when theclamping pressure begins to build up in chamber 43 oil pressure foractuating the pilot piston of valve 220 can then pass from line 270 toactuate valve 220. Oil under pressure from line 22S-221 and valve 264can then be directed to flow control valve 275278 to the cylinderchamber 53.

Valve 275 can be manually closed so that flow can take place to chamber53 only through check valve 278, but oil will then not be able to returnto the tank through valve 220. This serves the purpose of permitting theoperator to adjust the knife. Thus, cylinder 50 will pull the knife downwhen the buttons LH and RH are pressed, but when released, oil cannotexhaust from chamber 53 through closed valve 275 back to valve 220,although valve 220 has shifted to exhause position due tode-energization of SOL-2 and the internal spring in valve 220.Accordingly, the knife will be hydraulically locked in place. When valve275 is opened, spring 60 (FIGURE 1) will raise the knife forcing oilfrom chamber 53 through valve 275 and thus through valve 220 andultimately back to the tank.

It will be seen from the above that the system provides a simplicity anda power saving over systems which use respective pumps for the clamp andfor the knife. In the present system both pumps are working at all timeswhen hydraulic power is required for clamping and cutting, but only theoutput of the smaller pump section P2 is required when the machine isidling.

When the clamp is in top position, a cam operated valve 300 opens theexhaust of relief valve 252 to the tank so that the low pressure(approximately p.s.i.) prevails when the clamp is up, thus furtherreducing the motor load and therefore the heating effect on the oil.

Alternatively, 300 may be omitted and the exhaust or' 252 piped to 301where the operation of 222 will connect 252 to tank.

All switches of the control circuitry are of conventional constructionand it will be understood that although they are described as separateswitches, they may be of well known combined construction.

Likewise all valves are of well known conventional and commerciallyobtainable construction hence detailed deneription of their mechanicalconstruction is not required.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothese skilled in the art. Therefore, this invention is to be limited,not by the specie disclosure herein, but only by the appending claims.

What is claimed is:

1. In a paper cutting machine of the guillotine type, a knife actuatingmechanism comprising a single-ended power cylinder means, a knife barlfor supporting a knife, linkage means connecting said single-endedcylinder means to said knife bar for actuating said knife bar in acutting stroke when pressure is applied to said cylinder means, a springmeans connected to said linkage means and adapted to be stressed therebywhen said knife bar is performing a cutting stroke in order to effect areturn movement of said knife bar when pressure is released from saidcylinder means; said linkage means comprising a bellcrank having threearms and a fixed pivot therefor, one arm being connected to saidcylinder means for effectlng pivotal action of said bellcrank lever whensaid cylinder means is provided with pressure, a second arm beingconnected for actuating said knife bar, and a third arm being disposedto stress said spring means.

2. In a machine as set forth in claim 1, and further including a dashpotdisposed to be abutted by said second arm to limit downward movement ofsaid knife bar.

3. In a machine as set forth in claim 1, said spring means being acompression spring, a rod through said spring, an end of said rod beingconnected to said third arm, said spring having an end abuttable by aportion of said rod to be compressively stressed thereby when saidbellcrank lever is pivotally actuated by said cylinder, and a resilientbumper means disposed adjacent the third arm to be abutted thereby foreffecting a stop position in upd ward movement of said knife bar aseffected by said spring.

4. ln a machine as set forth in claim 1, including a dashpot disposed tobe abutted by said second arm to limit downward movement of said knifebar, said spring means being a compression spring, a rod means throughsaid spring, an end of said rod means being connected to said third arm,said spring having an end abuttable by a portion of said rod means to becompressed thereby when said bellcrank lever is pivotally actuated bysaid cylinder means and a resilient bumper means disposed adjacent thethird arm to be abutted thereby for effecting a stop position in upwardmovement of said knife bar as effected by said spring.

5. A control circuit for a guillotine type paper cutter having a clampand knife, comprising a knife control solenoid, a clam p controlsolenoid, a relay and respective contacts of said relay in seriescircuit with said solenoids and another contact of said relay in seriescircuit with said relay, a pair of manually operable switches eachhaving a first contact element in series circuit with said relay, andhaving a second contact element in series circuit with said knifecontrol solenoid, and having a third contact element in series circuitwith said clamp control solenoid, said first contact element beingnormally closed, said second and third contact elements being normallyopen and requiring manual force to be held closed while said firstcontact element is being held open, clamp operated switch means, knifeoperated switch means, said switch means having switches connected insaid circuit to said relay and said solenoids wherein said relay isenergized when the clamp and knife are in raised position through saidother contact of said relay and said first contact element of saidmanually operable switches; and wherein said solenoids are energizedwhen said manually operable switches are manually operated and thecircuit through said rst contact element of said manually operableswitches is then broken; and wherein said relay and said solenoids arethen energized through said clamp and knife operated switch means andsaid respective contacts.

6. The control circuit of claim 5, wherein energization of said knifecontrol solenoid and said clamp control solenoid causes said knife andclamp, respectively, to move toward a cutting and clamping position,respectively, and de-energization of said respective solenoids causessaid knife and clamp to return toward their resting positions; andwherein said respective contacts of said relay are normally open, andare only actuated to their closed circuit conditions in response toenergization of said relay; whereby if said relay becomes de-energized,said respective contacts thereof will revert to their normally opencondition to open the series circuits with said solenoids to causede-energization thereof to effectuate the return movement of said knifeand clamp.

7. A control circuit as set forth in claim 5, said knife operated switchmeans comprising a switch responsive to knife return movement andconnected to de-energize said clamp control solenoid, and said knifeoperated switch means having a switch connected to de-energize saidknife control solenoid when said knife reaches the end of a cuttingstroke, said relay being cle-energized when said knife control solenoidis cle-energized, wherein said relay is again energize upon release ofmanual force on said manually operable switches.

S. A control circuit as set forth in claim 5, one of said switch meanscomprising a switch shunting a contact element of one of said manuallyoperable switches and being operable upon initial cutting movement ofsaid knife to shunt said contact element so that said one manuallyoperated switch may be released.

9. A control circuit as set forth in claim 7, said knife operated switchmeans comprising a switch connected to shunt the second contact elementof one of said manually operated switches after the knife starts acutting movement so that said one manually operated switch may bereleased.

itl. A hydraulic system for operating a clamp of a paper cuttercomprising a high volume pump and a low volume pump having separateoutlets connected in parallel, a normally open shunt valve connected toconduct fluid to a tank from the outlet of said large volume pump, acheck valve connected between the outlets of said pumps whereby outlethuid from said large volume pump only can pass to said shunt valve, anoutlet means from said pumps, and valve means connecting said outletmeans to conduct fluid pressure to and from clamp cylinder means,control means having elements responsive to initial clamp movementtoward a paper pile from a rest position for closing said shunt valvewhereby fluid pressure is supplied to said valve means from both pumps,said control means comprising said valve means whereby said clamp ismaintained in said rest position by discharge from only said low volumepump through said valve means with outlet ow of said high lvolume pumpbeing shunted through said shunt valve.

11. The hydraulic system of claim 1t), wherein said control meansincludes an energizable solenoid which closes said normally open shuntvalve in response to energization thereof, said solenoid being energizedin response to one of said elements being operated iu response toinitial clamp movement toward a paper pile, whereby if said solenoid isfle-energized during operation of said clamp said shunt valve willrevert to its normally open condition to conduct huid from the outlet ofsaid large volume pump to said tank, whereby only outlet uid rom saidlow volume pump will he discharged through said outlet means to operatesaid clamp.

12. ln a paper cutting machine, a reciprocable clamp, hydraulic meansfor moving said clamp down and returning it to its starting topposition, a reciprocable knife, hydraulic means for moving said knifedown for cutting, spring means for returning said knife to its Startingtop position and holding it there, pump means for supplying highpressure and volume of oil to move said clamp and knife downwardly andfor supplying low volume to hold said clamp in its top position.

'13. ln a paper cutting machine as set forth in claim 12, said pumpmeans including a high volume pump and a low volume pump having separateoutlets connected in parallel, shut valve means for conducting fluidfrom said high volume pump to a tank when said clamp is in its topposition, and control means for closing said shunt valve means when saidclamp and said knife are to be moved downwardly whereby the combinedoutput of said high Volume pump and low volume pump will be utilized tomove said clamp and knife downwardly.

References Cited UNITED STATES PATENTS 2,400,996 5/1946 Iverson 83-639 X2,664,860 l/l954 Levetus 83-639 X 3,118,338 1/1964 Barley 83-639 X3,182,542 5/1965 Cochran 83--461 X 2,278,713 4/1942 Riddle 83-3802,825,404 3/ 1958 Barley 83-390 3,173,327 3/1965 Rupp 83-588 3,272,0509/1966 Barley 83-390 FOREIGN PATENTS 452,317 8/1936 Great Britain.

ANDREW R. JUHASZ, Primary Examiner.

